mendelian genetics the principles of probability can be used to predict the outcome of genetic...
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Mendelian Genetics
The principles of probability can be used to predict the outcome of genetic crosses
Probability - The likelihood that a particular event will occur is called probability.
When a baby is born, the probability that it is a girl is 1:2 or 50%.
Probability and Genetics
Probability and Product Rule: How do you calculate the probability of
more than one event occurring? Product Rule = Multiply the probability of
each independent event together
Probability and Genetics
Example: What is the chance that a couple (both heterozygous for tongue rolling) will produce a baby girl who can roll her tongue?
Probability and Genetics
Begin by determining the probability of each event happening independently:
What is the probability of producing a baby girl? ____________50% or 1/2
Probability and Genetics
What is the chance that a couple (both heterozygous for tongue rolling) will produce a child who can roll its tongue?
Set up a Punnett Square!
________________
R r
R
r
RR Rr
Rr rr
75% or 3/4
Probability and Genetics
The original question: What is the chance that a couple (both heterozygous for tongue rolling) will produce a baby girl who can roll her tongue? ________________
What is the chance that this couple will produce a baby girl who cannot roll her tongue? ________________
½ x ¾ = 3/8
½ x ¼ = 1/8
Gregor Mendel Mendel began his genetic
research by crossing true-breeding pea plants, the P(arent) generation.
The result of this cross is the F1 generation, which are hybrids.
He next crossed the F1 generation to produce the F2 generation.
Mendel’s Genetic CrossesF1
generationF2
generationP
generation
Mendel’s Research on 1 Trait
What is the phenotype ratio of F2 generation?
What is the genotype ratio of F2 generation?
3 violet flowers:1 white flower
1 BB: 2Bb: 1bb
Mendel’s Law of Segregation
Mendel recognized that each pea plant had two alleles for a trait.
He hypothesized that one allele came from each of the two parent plants.
Mendel’s law of segregation states: Allele pairs separate during gamete (sex cell) formation, and randomly unite at fertilization.
Production of Gametes
Half the number of
chromosomes as the parent
cell
The Two-Factor Cross Mendel next tested whether the
segregation of alleles for one trait (example seed shape: round or wrinkled)
affects the segregation of a second trait
(example seed color: yellow or green)
The Two-Factor Cross
One plant was true breeding for both yellow AND round seeds = P generation
This plant’s genotype was YYRR The only alleles that could be produced by
this plant were… Pass out whiteboards!
The Two-Factor Cross
The second plant was true breeding for both wrinkled AND green seeds = P generation
This plant’s genotype was yyrr The only alleles that could be produced by
this plant were… yr
The Two Factor CrossThe only possible result of this cross is …
RrYy = F1 generation What is the
phenotype of the offspring?
Round and yellow seeds.
YR YR
yr
yr
YyRr
YyRr
YyRr
YyRr
The Two-Factor Cross
Mendel next crossed the offspring of the F1 generation. He crossed YyRr with YyRr. Each plant is called a dihybrid.
Which alleles are created from YyRr? Work this out on your whiteboard! YR yR Yr yr
The Two Factor Cross
Draw a 16 box Punnett Square to show the cross between YyRr and YyRr
Begin by showing
the possible alleles. Then fill in the
boxes!
YR yR Yr yr
YR
yR
Yr
yr
ryr
Two Factor Cross Results
The Two Factor Cross
What is the phenotype ratio for a two factor cross between dihybrids? Write on whiteboard!
___________dominant for both traits – yellow and round seeds
___________dominant for one trait and recessive for the second – yellow and wrinkled seeds
9
3
The Two Factor Cross ___________recessive for one trait and
dominant for the second – green and round
___________recessive for both traits – green and wrinkled
3
1
•Phenotype ratio – 9:3:3:1
Mendel’s Actual Results
Mendel’s 4th Conclusion
Principle of Independent Assortment - genes for different traits can segregate INDEPENDENTLY during the formation of gametes.
For example: A person can have blonde hair and blue eyes or brown hair and blue eyes. Hair color and eye color are inherited independently of each other.